1. Field of the Invention
The present invention relates to a method of processing a magnetic thin film consisting of a magnetic material containing Fe, Co or Ni.
2. Description of the Related Art
A magnetic thin film consisting of a magnetic material containing Fe, Co, or Ni has been conventionally used in a wide variety of magnetic devices such as a magnetic head, magnetic disk, magnetic bubble memory, magneto-optical disk, magnetic sensor and thin film inductor. Furthermore, future application of the magnetic thin film to a magnetic random access memory (MRAM) or spin polarization effect (SP) device is expected. To manufacture these magnetic devices, particularly, to make a thin film magnetic head, magnetic sensor, magnetic bubble memory, thin film inductor, MRAM, and SP device, a desired patterning of the magnetic thin film must be performed. Moreover, if the desired pattern of the magnetic thin film can be performed in manufacturing the magnetic disk or magneto-optical disk, the pattern can be used as a recording track having a shape anisotropy.
Hitherto, to process a magnetic thin film into a desired pattern, ion milling has been mostly employed. The ion-milling is a method using an inert gas such as Ar, which is ionized and accelerated so as to bombard the magnetic thin film. In the ion milling method, an etch rate increases with an increase in an ion density, and also anisotropic processing can be attained if a bombardment angle of ions is set appropriately. However, the ion milling method has not etch selectively, so that it is difficult to process the magnetic thin film having a considerable thickness. In addition, to process a large-size magnetic thin film in its entirety, a large-scale ion source is required. The use of a large-scale ion source is undesirable from an economical point of view and the scaling-up of an ion source entails a technical limit. Furthermore, during processing, part of the processed material is ejected into a gaseous phase and redeposition thereof onto the sidewalls of a mask is caused. As a result, it is difficult to form a fine pattern accurately.
To form a thin film magnetic head, a magnetic thin film having a predetermined pattern is formed directly by a plating method. A representative example is NiFe plating applied to the inside of a resist frame pattern. However, the plating method is disadvantageous in the following points: It is difficult to supply the plating material constantly to the pattern-forming region, so that the compositions of the plating solution inside and the outside of the pattern-forming region become different with the passage of time. Hence, it is conceivable that the plating method may not deal with the up-and-coming needs for forming a magnetic thin film pattern of submicron order.
In the meantime, a plasma etching method, especially, a reactive ion etching (RIE) has been studied with the intention of applying it in the magnetic thin film processing. The RIE is mostly used in an LSI fabrication process by virtue of its excellent etch selectivity and economical advantages. In the LSI fabrication process, RIE makes it possible to form a fine pattern since the activated reactive gas reacts with a generally-used LSI material and easily produces a reaction product having high vapor pressure. Whereas, in the case of processing a magnetic thin film by RIE using the same reactive gas generally used in the LSI process, the product resulting from the reaction between the reactive gas and a magnetic material has low vapor pressure. Therefore, the magnetic thin film must be heated to high temperature to form a fine pattern, which prevents RIE from practical application to processing the magnetic thin film.
For example, processing of a magnetic thin film consisting of Fe--Si--Al by RIE using an activated chlorine-based gas is reported in IEEE Trans. Magn. 27 (6), 4888, 1991 and Jpn. Pat. Appln. KOKAI Publication No. 3-97877. These publication disclose CCl.sub.4, Cl.sub.2 and CCl.sub.3 F as the chlorine-based gas. However, to process the magnetic thin film at an etch rate as high as 100 nm/min or more, a substrate has to be heated to 300.degree. C. or more. Therefore, above method cannot be employed in manufacturing process of a magnetic device.
In the above method, removal of an etching residue has a trade-off relationship with prevention of side etching. In this case, just-etching is applied to avoid side etching and improve the patterning accuracy. However, the just-etching leaves a residue, so that further treatment is required thereafter to remove the residue. Hence, the above method is not practical.
Another technique for use in processing magnetic thin film consisting of the magnetic material containing Fe, Co or Ni is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 4-129014. In this method, the magnetic thin film is processed by supplying a gas mixture of a rare gas and Cl.sub.2, CCl.sub.4, CHCl.sub.2 F or CCl.sub.2 F.sub.2 to the exposed portion of the magnetic thin film. However, this method is not practical, since the etch rate, 20 nm/min, is extremely low. In this method, a magnetic material reacts with a chlorine-based gas to produce a chloride as a reaction product on the exposed portion of the magnetic material. However, in principal, the exposed portion of the magnetic thin film is physically etched by the rare gas, and hence the etch selectivity is low. In addition, due to the redeposition of processed material, the accuracy of processing is lowered.